Arsène Wenger will conduct a comprehensive investigation into his club's training methods and medical procedures in an effort to establish whether Arsenal could have avoided the spate of injuries that risks sabotaging their season.

The manager admits he is "concerned" that Arsenal will go into Sunday's north London derby shorn of at least four key players, after Mesut Özil joined a casualty list that already featured Aaron Ramsey, Theo Walcott and Jack Wilshere. A hamstring strain forced the German to limp off at half-time in Arsenal's Champions League draw with Bayern Munich on Tuesday and will keep him out of action for between three and six weeks. Thus the £42m summer signing will miss not only the match with Tottenham Hotspur, but also the pivotal meetings with Chelsea and Manchester City. It was hoped that Ramsey, at least, would be fit in time for those fixtures but his participation now also looks in jeopardy as he struggles to recover from a thigh problem that has incapacitated him since Boxing Day.

"I am concerned that this happens," said Wenger. "If you look at our overall injury list going into such a decisive part of the season, we have not Wilshere, not Walcott, not Özil, not Ramsey and we went to Bayern without [Kieran] Gibbs and [Nacho] Monreal. We are analysing very deeply why it happened and to see if there is a link between all these injuries."

In a season in which Alex Oxlade-Chamberlain, Yaya Sanogo and Nicklas Bendtner have also been stricken for long periods, the manager is especially worried about the frequency with which his players succumb to muscular injuries of the sort that have afflicted Ozil, Ramsey and Gibbs.

"For Walcott it's completely bad luck. Wilshere – I don't think it is linked with the other injuries, it's more linked with his history and the kick he got. But the rest, maybe we have to find why it happened." Asked whether he would review his training and medical procedures, Wenger said he would assess "everything".

"It's very difficult to find any obvious reason why. For example, a player like Özil –he was rested against Stoke, then he goes to Germany and he trains different, sometimes on a different ground with different sessions. He played the whole game [for Germany against Chile] and the whole game for us against Everton and he produced on that day, doing more physically than usually and he paid for it the next day. Why? I don't know."

The manager said he was especially bothered about Ramsey's lingering thigh trouble. "That's our worry at the moment, Ramsey is taking longer than expected," he said. "He had a first setback and then he planned to join in [training] on Thursday but he had recurring pains in his thigh. Of course he's now a little apprehensive because of the setback. We have to be very cautious with him. When will he be back? I believe it's two more weeks now."

In better news for Wenger, Kim Kallstrom is available to make his long-awaited debut on Sunday. Arsenal fans were underwhelmed when, at a time when they were crying out for another striker, Wenger made a 31-year-old midfielder with back trouble his only January signing. But given the current injury problems, Kallstrom's availability is well timed. If the Swede who arrived from Spartak Moscow can recover his match sharpness quickly, he could make an important contribution to Arsenal as the campaign reaches its climax.